Hiding Zaha's pipes

The Zaha Hadid Architects-designed Glasgow Museum of Transport on the River Clyde is 54 weeks into its 129-week building programme. The competition-winning design was conceived as a seamless object, the first renders suggesting a walk-in sculpture cast in chrome. As the budget spiralled to £74 million, a stainless-steel shingle roof was dropped in favour of zinc standing seam, which will be constructed next month. But the initial idea of a ‘building with no backside’ and an unobstructed roofline has been retained, meaning servicing had to be accommodated within the roof and under the ground.

Roof and walls have the same warm-roof detail. The seamless curved transition is detailed using 9mm wooden battens, curved and crossed in two directions. ‘Everything happens within the 1.2m thickness of the envelope: fire, light, ventilation and drainage,’ says project architect Johannes Hoffmann.

‘We reduced the plant room from 30 to 15 per cent of the building’s 11,200m² footprint by working with the conservation team and increasing the usual 1ºC temperature tolerance to 3ºC,’ says Scott Baird, associate director of building services engineering at Buro Happold. The complex geometry meant the air-handling units, chiller and ducts could not be contained within or on top of the roof.

‘The offsets between roof surface, structure and internal lining are not all the same,’ says Hoffmann. ‘They vary from 375mm to 800mm. The standard steel sections of the structural frame could not accurately trace the proposed roofline, so the secondary structure supporting the zinc cladding was built-up.’

Modelling software 3ds Max was the imaging platform for architect, engineer and steel subcontractor Watson Steel Structures. ‘If it hadn’t been for tender requirements we wouldn’t have drawn any standard sections at all,’ says Baird.

SERVICESInstead of feeding the air-supply ducts through the roof, ‘super trenches’ have been dug into the 300mm in-situ concrete slab to accommodate 2.5 x 2.1m ducts. These feed air to handling units at three places on the first floor from motorised grilles in the internal walls. The entire slab is piled (driven with both cast-in-situ and precast concrete) on a 3m x 3m grid, due to the high point-load exerted by some of the exhibits.

The chiller unit is installed in one of two first-floor plant rooms. To enable air to circulate there is a large hole in the roof frame, through which the unit will be also accessed for maintenance and future replacement. The zinc cladding continues the line of the roof to conceal this hole but is 40 per cent perforated.

Due to inevitable storm-water ingress, the plant room is detailed as an external space with waterproofing and hard ducting. Drainage of the roof is achieved with syphonic drainage in the ‘valleys’, gravity drainage at the perimeters and hidden downpipes in the structural steel mullions of the north and south-facing glazed facades.

Shadow gaps have been designed in the 9,500m² internal lining that define the geometry; act as movement joints; provide an accessible home for cabling; and divide the area into manageable sections. The perforation detail has yet to be finalised but will continue the theme from the roof and improve acoustic performance by reducing reverberation time.

CLADDING PREPARATIONS AND MOCK-UPS‘Subcontractors are willing to spend more time and money to get it right,’ says Jim Ward, site manager for main contractor BAM.The seams of the Rheinzink zinc cladding have been laid out by the architect and a full-scale mock-up of some of the most difficult areas is currently awaiting final approval.

Subcontractor Vala has worked to perfect the crimping detail and area around window openings, and has set up a workshop on site in preparation for the16,000m2 job, which will take approximately 42 weeks to complete.

An 18m-long mock-up section of the curved interior ceiling lining - perforated polymer-modified, glass-reinforced gypsum supplied by British Gypsum - has been built in Barnsley by Clark & Fenn Skanska.

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